Structural characterization of the members of a polymer series, compatible solutes in Anabaena cells exposed to salt stress

Abstract

In response to salinity cyanobacteria synthesize different osmoprotective compounds. We had reported that Anabaena cells accumulate not only sucrose (Suc) but also fructose-containing oligosaccharides in the presence of NaCl and at stationary phase (Plant Sci. 167 (2004) 1003–1008). In the present study, using NMR and GC–MS we showed that the oligosaccharides previously described are members of a new series of non-reducing Suc derivatives, where glucose (Glc) is linked through its hemiacetalic hydroxyl to the 2 position of the Glc moiety of Suc, resulting in the general structure: [α-d-Glcp-(1 → 2)]n-α-d-Glcp-(1 → 2)-β-d-Fruf. In the continuous series, it was possible to identify members with up to 10 hexose residues, depending on the cell analysed. As each member of the series has only one Fru, that of the terminal Suc molecule, we called these polymers with the general name of sucroglucans. Their occurrence was investigated in representative cyanobacteria of different taxonomic groups either unicellular or filamentous strains, including nitrogen-fixing and non-fixing strains. The oligosaccharides were mainly detected in salt-treated cells of Section 4 strains. Therefore, together with Suc, the members of the sucroglucan series should be included among the compatible solutes synthesized in response to salt stress in filamentous cyanobacterium strains.